Walkers rest amid the trees at Island Center Forest on Vashon Island, which is part of King County. Many trees around Western Washington are struggling, including Western hemlock on Vashon, likely from drought stress. Photo by Susie Fitzhugh

Environment

King County forests are facing new challenges

Hot, dry summers are stressing native tree species in Western Washington.

Western Washington’s forests are one of the main attractions for residents and visitors looking to escape the grind of the city, but the expanse of rolling trees are facing increasing challenges.

Western Washington and especially Puget Sound have a variety of forests and conditions which affect them. Some areas like Vashon Island were extensively logged during and after World War II, and much of the region has a history of intensive commercial farming. One of the legacies of this are dense stands of tree plantation forests, where the trees are close together and often hardwood varieties that wouldn’t naturally occur.

On Vashon, in particular, much of the island was logged around 80 years ago and saw farmland built out. Much of the farm economy has since disappeared, and alder trees began filling in the island. However, alders have a lifespan of around eight decades, meaning much of the forests are dying and being dominated by undergrowth like Scotch broom and blackberry bushes. These are considered weeds and help choke out the island’s native western hemlocks, which used to be one of the dominant tree species on the island.

“If we don’t actively go in and replant those areas with other species, they will never return to forest,” said Tom Dean of the Vashon Maury Island Land Trust.

Western hemlock are struggling, seemingly from drought stress, Dean said. Hemlock thrive in shade and particularly when they are around conifers. When surrounding trees are cleared, it can damage and shock hemlock. Dean said they’ve stopped planting hemlock because of this.

Longer, hotter and drier summers are likely affecting forests in other parts of King County, said David Kimmett, the county’s open space and natural lands program manager.

“We’re starting to see some Western hemlock die off, and again, that could be attributed to some of the long, hot summers we’re seeing. The question is are we going to see these long hot summers on a regular basis,” Kimmett said.

Other species are being affected too, particularly hardwood varieties, which may not be as drought tolerant or able to cope with low soil moisture. To combat this, Kimmett said the county has begun replanting Douglas fir, which are native trees that are both drought tolerant and more effective at scrubbing carbon from the atmosphere.

Part of this involves the county’s 1 Million Trees program, which the county is hoping to finish by 2020. As of last week, more than 750,000 trees had been planted.

Kimmett said the county inherited many former tree plantation sites. These are former tree farms or logging patches where the natural trees were clear cut, and largely hardwood varieties were planted in dense formations. These choke out light to the forest floor and allow fires to more easily jump between trees. Many of these plantations contain only one species of tree and provide limited amounts of wildlife habitat.

Conservation Northwest spokesperson Dave Werntz said following fires in southern Oregon, researchers found that plantation sites saw more severe burning.

“Plantations are probably the number one forest health issue on the west side,” Werntz said.

Forest health on federal forest land has been a priority for the U.S. government for a few decades, and has been actively managed more than private lands, Werntz said. However, since the end of World War II up until the 1980s, there had been an effort to convert old-growth forests to plantations, so a legacy of this conversion remains even on federal lands.

In response, the county has begun going in and thinning out these plantations to let in sunlight, improve access for wildlife and help diversify the forests. Additionally, if forestland is switched from hardwood to conifer species, it allows the forests to soak up more carbon, Kimmett said.

“They gobble up more carbon,” Kimmett said. “It’s a sort of genetic trait, and it is well documented in the research. … It’s one of those sort of benefits that comes from Douglas firs.”

On top of this, many of the tracts were planted with red alders, which generally don’t live longer than 100 years; many of these aging trees in King County are being replaced by conifers, which can live for more than 300 years. Werntz said forests in the Pacific Northwest are able to store more carbon than many other forests across the globe, especially if they are allowed to return to old-growth forests.

“The efforts that have been made thus far to restore the plantations that had been established are impoving our ability to withstand the effects of climate change,” Werntz said.

In addition, Sarah Brandt, who works with the county’s Parks and Open Spaces program, said they are working to promote the county’s land conservation initiative. Passed last year, the initiative set a goal of acquiring 65,000 acres of land over the next 30 years for preservation. This includes not only forests, but farmland and open space, too.

These conservation efforts could become more important in coming years as drought has become more frequent. Glenn Kohler is a forest entomologist with the Washington State Department of Natural Resources and said while forests are generally healthier in Western Washington when compared to those on the east side of the state, lack of water and heat are affecting them.

Droughts have become hotter and have lasted longer in recent years, Kohler said, and the number of days with temperatures over 90 degrees have been increasing. Trees in the Pacific Northwest can handle some years with high temperatures and a lack of water, but when these summers become more frequent, the trees end up with a water deficit. This wilts them, but also makes them more susceptible to insect infestations.

Trees use pitch and resin to push out insects, but when they are heat stressed or living with a water deficit, they are less able to resist bugs. The state has been finding bark beetles and wood boring beetles attacking trees and the widespread root rot disease may be increasing.

“For the most part, what we’re seeing is insects and diseases that are ordinarily kind of secondary — they are becoming more common, and that’s just because they could not kill or damage a healthy tree, but these weakened trees are more susceptible to them,” Kohler said.

Despite its other advantages, the Douglas fir is vulnerable to root rot and infestations, especially younger trees. It can be hard to track forest health from one year to the next since the state doesn’t use imagery to track forest health. Instead, the state flies experts around over the forests each year to survey their health.

“We are seeing increases in the survey data in the bark beetle activity, and bark beetles are one of those insects that would be pitched out by a healthy tree that has a lot of water,” he said.

Outbreaks of beetles in particular in Western Washington can be tied to natural occurrences as well, like windstorms. Following large windstorms around a decade ago, the state saw a large outbreak of beetles in the forests.

Another concern for local forests is an increase in wildfires west of the Cascades. Already this year, nearly 50 fires were started in Southwest Washington during a streak of 80 degree days in March. While fires are relatively rare in the western areas of the state compared to Eastern Washington, they can become severe if conditions are right. Much of the focus in Western Washington in coming years will likely be in the urban-wildland interface, where human development runs right up to forested land.

Kohler said more education will be needed to get landowners to understand how to adapt to the possibility of increasing wildfires.

The National Interagency Fire Center recently released its fire outlook for April through July for King County. It showed that much of Western Washington will be more prone to wildfires than usual. The previously mentioned fires in Southwest Washington this year burned around 272 acres and were mainly started by people burning yard waste.

Precipitation this year was generally above average across most of the western U.S., and as the spring greening begins in April, mountain snowpack will begin to melt. If snow melts at normal or slower than average rates, it can postpone fire season, but if it melts faster than normal, forests at higher elevations could catch fire sooner. In lower elevations, lots of winter and spring moisture will likely mean more grass, which will dry and become fire-ready across the region in May and July.

Last year in Washington state there were 1,744 fires that burned nearly 429,000 acres. Of those, 1,457 were human-caused, accounting for nearly 280,000 of the acres burned. The state’s Department of Natural Resources is asking for a historic $55 million for wildfire response in this year’s budget and is planning on treating some of the 2.7 million acres of diseased and dying forestland across the state.

The state is also watching for invasive species that haven’t yet colonized forests in the Pacific Northwest, Kohler said. In particular, the gypsy moth isn’t established in the area, but the rolling forests of Washington state is an ecosystem where they could thrive. Already on the East Coast of the U.S. and Canada, the moth has been damaging hundreds of thousands of acres of land, and egg pods could be unintentionally transported by people traveling across the country. The Department of Agriculture conducts eradication projects to try and prevent the moths from setting up in the state.